The present invention relates to an input buffer circuit for detecting the frequency or angular information of an electromagnetic pickup coil in terms of a voltage.
In a known input buffer circuit of the above type, the voltage signal from a pickup coil is reshaped through a CR filter and then subjected to voltage comparison by a comparator. The CR filter circuit is an essential circuit element for the purpose of eliminating any noise signal superposed on the signal line of the pickup coil. However, where the time constant of the CR filter circuit is increased, if the signal frequency is high, the signal voltage from the pickup coil will be delayed in phase, thus making it impossible to obtain an accurate angular information. In other words, there is a disadvantage that if the time constant of the noise suppressing CR filter circuit is increased so as to improve the antinoise characteristic, the resulting angular information and detection response characteristic will be deteriorated.